06Class 12 Biology
Evolution short notes
Short notes on the origin of life, evidence for evolution, natural selection, Hardy-Weinberg and human evolution.
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Origin of life
- Oparin and Haldane proposed chemical evolution, and Miller's experiment made amino acids from simple gases.
- Early cellular life appeared about 2000 million years ago, according to NCERT.
Evidence
- Homologous organs share an origin but differ in function, which is divergent evolution. Examples: forelimbs of whales, bats and humans.
- Analogous organs have similar functions but differ in origin, which is convergent evolution. Examples: wings of butterfly and bird.
- Industrial melanism in peppered moths shows natural selection in action.
- Antibiotic and pesticide resistance show the same process.
- Adaptive radiation: Darwin's finches and Australian marsupials.
Mechanisms
- Darwin: branching descent and natural selection.
- Lamarck: use and disuse of organs, which is no longer accepted.
- Hugo de Vries: mutation can cause sudden change (saltation).
- Hardy-Weinberg: p² + 2pq + q² = 1, and allele frequencies stay stable unless something disturbs them.
- Five factors disturb it: gene migration, genetic drift, mutation, genetic recombination and natural selection.
Human evolution
- Dryopithecus and Ramapithecus came first, about 15 million years ago.
- Australopithecus lived about 2 million years ago in Africa.
- Homo habilis: brain 650 to 800 cc.
- Homo erectus: about 900 cc.
- Neanderthals: about 1400 cc.
- Homo sapiens arose in Africa.
Where students slip up
- Mixing up homologous (divergent) and analogous (convergent).
- Using 2pq as a single allele's frequency. It's the frequency of heterozygotes.
- Getting the order of human ancestors wrong.
Try it on your weakest chapter.
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